It is known to design front covers of electrical appliances such as, for example, ovens or the like, in particular with at least one front cover opening such that a rotary encoder of an operating device can be attached behind the front cover. The rotating shaft of said rotary encoder projects through the front cover opening and a rotary knob is fitted thereon on the front side. In order to be able to illuminate this operating device or the rotary knob, for example to display information to an operator, it is possible according to EP 1 898 184 A2, to arrange LEDs on a printed circuit board of the rotary encoder. By means of lightguides, the light passes through a housing of the rotary encoder, a holding device and through the front cover to the rotary knob and to a ring surrounding the rotary knob.